Synchronizer for multiple set radar systems



1950 c. w. BROWN 2,516,296

' smcmouxzna FOR MULTIPLE ss'r RADAR SYSTEMS Filed May 3. 1949 HM FIG. I

MASTER r0 mmve AIvo TRIGGER OSCILLATOR ULTMBRATOR CIRCUITS or RADAR $51I LOW -PASS RJFILTER TRIGGER CIRCUIT OF RADAR SET 2 FIRST RADAR FIG. 2

(TRANSMISSION LINE L I =--EXTERNALLY$UPPLIED f- SYNOHRONIZING VOLTAGEPHASE-SHIFTIN T0 TRIGGER AND SYNCHRONIZING MASTER OSCILLATOR TIMINGAMPLIFIER\ MULTIVIBRATOR LOW PASS FILTER OATHODE F OLLOWE R INVENTOR.THIRD CARL W. BROWN RADAR \OUTPUT TRANSMISSION LINE L ATTORNEY 7SYNCI'IRONIZING SYSTEM 2 I PHASE SHIFTING NETWORK l t, 20 i 1H5 I DRIVERI MASTER OSCILLATOR AMPLIFIER MULTIVIBRATOR AND Patented July 25, 1950SYNCHRONIZER FOR MULTIPLE SET RADAR Carl W. Brown, Silver Spring, Mdassignor to the United States of America as represented by the Secretaryof the Navy Application May 3, 1919, Serial No. 91,083

. 1 This invention relates to a multiple set radar system. Morespecifically, it relates to means for synchronizing the operation ofseveral similar radars closely adjacent one another and having the samepulse repetition frequency, and to the process employed.

In order to operate several radar equipments simultaneously at about thesame frequency and in close proximity to each other (as aboard a ship),it is necessary to provide some means of synchronization of theirtransmitting periods so as to provoke a minimum of interference with oneanother.

The rate at which pulses are transmitted is commonly controlled by amaster multivibrator circuit in the radar equipment. This circuit, inturn, may be synchronized by a sine wave voltage of slightly higherfrequency than that of the multivibrator. Thus, the exact time oftransmission can be controlled by an external master oscillator of theproper frequency. Furthermore, by means of a phase-shift circuit, asecond radar transmitter having substantially the same pulse repetitionfrequency can also be made to transmit at a time different from that ofthe first transmitter, due to this phase shift. This permits the secondradar system to transmit at a time such that its transmission causes aminimum of interference with the first radar system, and vice versa.

Because of the scarcity of external master oscillator units, it wascustomary to tolerate the interference produced by adjacent radar sets.

The present invention was designed for use in place of the externalmaster oscillator and is to r be incorporated into the circuit structureof each 7 Claims. (01. 343-5) set of a system of standard radars. Theinvention is utilized to derive a synchronizing control voltage from themaster oscillator multivibrator of each of the radar sets and to applythe derived control voltage to the next succeeding set, for controllingthe relative time of transmission of each set in the system.

Therefore, it is an object of the present invention to providesynchronous operation of adjacent radar sets having substantially thesame pulse repetition frequency.

Another object of this invention is to eliminate the need for a separateexternal master oscillator of a synchronously operated system of radarsets.

A further object of this invention is to provide synchronous operationof a system of standard radar sets without substantial modification ofthe circuit structure of the individual sets;

Other objects and many of the attendant advantages of this inventionwill be appreciated readily as the same becomes understood by referenceto the following detailed description, when considered in connectionwith the accompanying drawings, wherein:

Fig. 1 shows a block diagram of the invention adapted for general use,and

Fig. 2 shows a block diagram of a modification of the invention adaptedfor use on a "Mark 39," fire control radar.

More specifically, Fig. 1 shows a pair of free running multivibrators I,ll of general construction, which constitute the master oscillators ofstandard radar sets. Each of multivibrators I, I I has a'square wavevoltage output I'll, III, the frequency and period of which isdetermined by the values of the parameters of the multivibratorcircuits. The operation of the multivibrators may be further controlledby a synchronizing control voltage applied to the control grid of one ofthe electron tubes in the multivibrator circuit. For optimum operationthe period of the synchronizing voltage should be slightly less than theperiod T of square waves l0, 2.

The square wave output of multivibrator I is fed to the trigger andtiming circuits of radar set No. 1 and to the input of low pass filter3. Low pass fllter 3 is of standard construction and may comprise an RCcircuit tuned to pass the fundamental frequency of the multivibrator.The filter 3 serves to filter out the higher harmonics present in squarewave ill and to derive a sine wave l2 of fundamental frequency in itsoutput. It should be understood that the output voltage of themultivibrators may be something other than the exact square waveillustrated but this would not alter the operation of the present systemso long as the fundamental frequency remains the same.

The output of low pass filter 3 is coupled to the input of cathodefollower 4, the output of which is coupled through transmission line Lto the input of phase shifting network 5. Cathode follower 4 serves tomatch the relatively high impedance output of filter 3 to the relativelylow 3 impedance input of transmission line L and phase shifting network5. serves to interconnect the two radars whose relative operation is tobe controlled and may be of varying length.

The phase shifting network 5 may comprise a transformer having a centertapped secondary connected in parallel with a series combination of acapacitor and a variable resistor, however any of the known variablycontrolled phase shifting networks would serve equally as well for it isnot intended to restrict the circuit to any specific construction.Variable phase shifting network 5 serves to shift the phase of thederived sinusoidal wave I? a desired number of degrees thereby toprovide a means for adjustably. controlling the time of firing of themaster oscillator multivibrator ll with respect to the time of firing ofmaster oscillator multivibrator l.

.The output of phase shifting network 5 is coupled to the input ofdriver amplifier 6 and the output of driver amplifier 6 is coupled tothe input of the synchronized multivibrator II. The output ofmultivibrator l I is connected to its respective trigger and timingcircuits and to a second synchronizing circuit I. Synchronizing circuitl is similar in construction to circuit 2 and therefore is not describedin detail. Driver amplifier 6 serves to amplify the phase shiftedsinusoidal control voltage to an amplitude sufllcient to insure itscontrol over the time of firing of the synchronized multivibrator H.

In order to insure control over the time of firing of multivibrator H,and thereby provide the optimum operation of the system previously mentioned, the period of the amplified synchronizing voltage M should beslightly less than the period of the output waveform of multivibrator M.This relation may be achieved'by adjusting the, frequency of oscillationof multivibrator H to be slightly lower than the frequency of controlwave it. A difference in frequency of one or two cycles would sufiice toinsure proper control. The output of multivibrator it may then be fed toits respective timing and trigger circuits and through synchronizingcircuit l to control the time of firing of the next succeeding radar setin the system.

Any desired number of radar sets may be synchronized in their operationby use of the present invention. As many as four units have beenoperated simultaneously without any interference difiiculties and moreunits may be operated if a slight increase in interference is tolerated,or if the individual units are located judiciously with respect to oneanother.

Fig. 2 shows a modification of the present invention adapted for use onthe "Mark 39 fire control radar. The modification shown in Fig. 2 classnot differ essentially from that shown in Fig. 1 but has been includedto show the preferred manner of constructing the present invention intwo sections and is shown broadly at 8 and 9. The sections 3 and 9 arebuilt into each individual radar set. Section B is connected to theinput of the master oscillator multivibrator i and includes the phaseshifting network 5 and driver amplifier 5 described with relation toFig. 1. Section 9 is connected to the output of the master oscillatormultivibrator and includes the low pass filter 3 and cathode follower 4described with relation to Fig. 1. Each of the elements 3, 5, 5, 5, L1and L2 of Fig. 2 functions in exactly the same manner as does itscounterpart in Fig. 1, therefore, a discussion of the manner of opera-The transmission line L tion of the embodiment of the invention shown inFig. 1 is thought to be a sufllcient disclosure of the manner ofoperation of Fig. 2.

The square wave output of multivibrators I, ll may be resolved into anintegral number of sinusoidal wave shapes in accordance with the Fourieranalysis of a uniformly repetitious wave. The waveform thus analyzedwould contain a fundamental (lowest) frequency equal to and an integralnumber of harmonies thereof. In the present invention the higherfrequency components of the square wave I0, 20 are eliminated and thefundamental derived as a sinusoidal control voltage in filter 3. Thesine wave voltage thus derived is coupled by means of a proper impedancematching network 4 through transmission line L to the phase shiftingcircuit 5 located on the radar set whose time of transmission is to becontrolled. Phase shifting network 5 shifts the phase of the sinusoidalcontrol voltage a desired number of degrees along the time axis. Theresultant phase shifted sinusoidal voltage is then amplified and appliedto the control grid of the master oscillator of the controlled radar setas a synchronizing control voltage thereby to control the time oftransmission of the controlled radar set relative to that of thecontrolling set.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is: y

1. In combination, a plurality of standard pulse modulated radar sets,means for deriving from one of said radar sets a sinusoidalsynchronizing control voltage, and means for utilizing said controlvoltage to control the time of another of said sets.

2. In combination, a plurality of standard pulse modulated radar sets,each having a master oscillator which controls the time of transmissionof its associated set, means for deriving from the master oscillator ofone of the sets a sinusoidal synchronizing control voltage, and meansfor utilizing said control voltage to control the time of transmissionof another of said sets.

3. The combination set forth in claim 2, further characterized in thatsaid means for util' ing the control voltage comprises a variable meansfor shifting the phase of the derived sinusoidal synchronizing controlvoltage a desired number of degrees, and means for applying the phaseshifted control voltage to the input circuit of the master oscillator ofthe next succeeding radar set.

4. The combination set forth in claim 2 further characterized in thatsaid means for utilizing the derived control voltage comprises avariable phase shifting means, an impedance matching means connectedbetween said means for deriving a sinusoidal control voltage and saidvariable phase shifting means, and means for applyin the phase shiftedcontrol voltage to the input circuit of the master oscillator of thenext succeeding radar set.

5. In combination, a plurality of standard pulse modulated radar setseach having a master oscillator which controls the time of transmissionof its associated set, a low pass filter circuit coupled to the outputof the master oscillator of one of said ra ar sets, a cathode followercoupled to the of transmission output of said low pass filter. avariable phase shifting circuit coupled to the output of said cathodefollower through a. transmission line, and a. driver amplifier coupledto the output of said variable phase shifting circuit, the output ofsaid driver amplifier being coupled to the input of the masteroscillator of the next succeeding radar set.

6. In combination, a source of rectilinear, unirormly repetitious waves.a low pass filter coupled to the output of said source of waves forderiving a sinusoidal wave therefrom, an impedance matching meanscoupled to the output of said low pass filter, a phase shifting networkcoupled to the output of said impedance matching means, and an amplifiercoupled to the output or said phase shifting network.

'I. In combination, a radar set having a master 6 oscillator whichcontrols the time of ton of the set, a low pass filter coupled to theoutput of said oscillator and an impedance matching means coupled to theoutput of said low pass filter: an amplifier coupled to the inputcontrol circuit of said master oscillator and a. phase shifting networkcoupled to the input of said amplifier.

CARL W. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PA'I'ENTS

